In related art, the content (roads, intersections, traffic signals, etc.) of the road map for use in navigation apparatuses has been obtained and updated by fieldwork. For example, a person in charge is assigned to each area, and each person in charge goes around the assigned area to verify the data (road information) of the content of the road map.
Regarding the intersections, when searching for a route, intersections provided with the road information (such as route regulation information) (herein referred to as the “reference intersections”) are associated with region data of an upper level so that such intersections are preferentially selected. Search efficiency and safety of route guidance have been increased in this manner. As used herein, the “route regulation information” includes “traveling in designated directions only,” “follow directions on lanes,” “no entry,” etc. Such road information is used to operate navigation systems. However, conducting field research on all the intersections as the reference intersections is not practical as it is extremely time-consuming and requires a very high cost. Thus, it is necessary to individually set standards to limit the number of intersections to be researched.
Moreover, a significant amount of time and cost is required to update such road information by human labor.
In order to save labor, techniques of automatically extracting an object to be updated are introduced in Patent Documents 1 to 3. In such techniques, probe cars are used to collect road information.